I recently had very strange issue and I felt almost lost. With windows phone project I was keep getting ‘System.IO.FileNotFoundException’ at some point after application is launched in Emulator (or Device). However My Build was successful. What I noticed that in my *.xap file which was deployed to Emulator (to see xap file content simply rename to *.zip).. there was one dll missing but it was there in Bin\Debug … so why my dll not packaged in XAP file ????
If you ever face this problem don’t even waste your time and go straight to the Project Properties Page and rename assembly name (default name space is fine) which is missing in XAP file.
I named one of my dll to MyApp.Resources.dll and VS2012 didn’t like it for some reason… As soon As I renamed it to MyApp.ResourcesXYZ everything started fine.
So moral of story … VS has some hidden bugs which can screw you really bad … Some of your dll name can conflict with inbuilt keywords and it can affect XAp file packaging so be careful what you write in “Assembly Name” attribute on Project Properties page.
Hope you find this useful !!!